Ramsey Electronics SCA1 User Manual - page 15
SCA1
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15
1. Install a fresh 9 VDC battery; an alkaline is preferred.
2. Push the power switch to the "on" position. The unit should draw about
20 ma from the 9 VDC source, without a speaker connected.
3. Using a frequency counter or oscilloscope connected to TP1, verify that
there is a square wave present. This square wave should be approximately
6v p-p. As you turn the "tuning" pot, R1, the oscillator frequency should
vary from about 50 kHz to 110 kHz. Don't be concerned if the range is not
exactly 50 to 110 KHz, just as long as 60 to 80 KHz is covered.
4. If you have access to an audio oscillator, you may apply a signal in the
50 to 100 KHz range to the input of the SCA1. While watching the TP1 test
point, you should see the frequency changing to match the applied signal.
5. Connect a small speaker to the SCA1's audio output jack, J3. With no
signal applied, you should hear a hiss similar to the interstation noise
heard on a standard FM radio. As the audio oscillator is tuned to the
frequency that the SCA1 is tuned to, you should hear a quieting in the
speaker.
These check verify almost completely the proper operation of the SCA1. We're
now ready to actually hook-up the SCA1 to an FM receiver.
HOOK-UP TO AN FM RECEIVER
Hooking up your SCA1 to an FM receiver can be easy or difficult and
frustrating. The Ramsey FR-1 FM broadcast band receiver has a convenient
baseband output for easy connection to the SCA1; other commercial FM radios
aren't quite as easy.
Hooking up the SCA1 to an FM receiver involves locating the baseband
demodulator output on the FM receiver. Some older tube-style FM radios have
what is known as a "multiplex" output jack. This jack was for connection of an
external stereo adapter. The multiplex output was nothing more than a buffered
output right from the receiver's FM detector. This output was not low-pass
filtered in any way and contained all the modulation information that was